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A 150-foot section of pavement on the highway buckled on Feb. 20 in what Arizona Department of Transportation engineers call a "geologic event."

After receiving environmental clearance, heavy construction began Tuesday as ADOT crews started cutting a pathway down to the base of the mountain slope.

The work is expected to take at least two weeks.

The access path will allow the geotechnical engineers to dig pits, approximately 20-40 feet long and 10-15 feet deep, which will provide critical information regarding any movement that may be present at the base of the slide.

The excavation work is necessary because it will lead to recommendations by the geotechnical team on what options are available within the site to realign the roadway or rebuild the existing roadway.

"This is the final piece of the puzzle we'll need to wrap up this geotechnical investigation," said Steve Boschen, ADOT deputy state engineer of design. "Prior to this, our drilling crews were only able to access this area via helicopters.

"ADOT's goal is to repair this critical section of highway and restore connectivity throughout the region as soon as possible. But before we can start the repairs, we need to determine the cause of the landslide and assess the safety of the slope."

ADOT's geotechnical investigation at the US 89 landslide site is the first phase of the solution. Crews are monitoring the stability of the slope and the ultimate repair of the highway will be based on the results of the geotechnical investigation. Efforts also continue on exploring the use of Navajo Route 20 as a temporary detour route while US 89 repairs are addressed.